Is Active Impedance the Key to a Breakthrough for Legged Robots?

This work addresses the question whether active impedance control is key to a breakthrough for legged robots. In this paper, we will talk about controlling the mechanical impedance of joints and legs with a focus on stiffness and damping control. In contrast to passive elements like springs, active impedance is achieved by torque-controlled joints allowing real-time adjustment of stiffness and damping. We argue that legged robots require a high degree of versatility and flexibility to execute a wide range of assistive tasks to be truly useful to humans and thus to lead to a breakthrough. Adjustable stiffness and damping in realtime is a fundamental building block towards versatility. Experiments with our 80 kg hydraulic quadruped robot HyQ demonstrate that active impedance alone (thus no springs in the structure) can successfully emulate passively compliant elements during highly-dynamic locomotion tasks (running and hopping); and, that no springs are needed to protect the actuation system. Here we present results of a flying trot, also referred to as running trot. To the authors’ best knowledge this is the first time a flying trot was successfully implemented on a robot without passive elements such as springs. A critical discussion on the pros and cons of active impedance concludes the paper. Claudio Semini and Marco Frigerio Dept. of Advanced Robotics, Istituto Italiano di Tecnologia (IIT), via Morego, 30, 16163 Genova e-mail: [email protected], [email protected] and [email protected] Victor Barasuol PPGEAS Dept. of Automation and Systems, Federal University of Santa Catarina (UFSC), Florianpolis, SC, Brazil e-mail: [email protected] Thiago Boaventura and Jonas Buchli Agile & Dexterous Robotics Lab, ETH Zurich, Tannenstr. 3, 8092 Zürich e-mail: [email protected] and [email protected] 1 Preprint to appear in 'Proceedings of International Symposium of Robotics Research (ISRR) 2013', Springer STAR Series